Pipe tapping devices are commonly recognized for the important role which they play in overcoming the need to shut down the operation of pipeline systems in order to join or repair branch fittings. Although the individual design of pipe tapping apparatus may differ amongst various devices disclosed by prior known art, the common function of such apparatus is to allow for the joining of new branch fittings without disruption to the through-flow of fluid in the main pipe.
Some disadvantages which are commonly presented by known pipe tapping devices include:
i) large dimensions and complexity of the apparatus used, which in turn, often result in increased production costs;
ii) difficulties associated with overcoming resistive forces where a large area of pipe wall is sought to be tapped;
iii) difficulties associated with tapping thick pipe walls, or pipes made of very hard materials;
iv) the time taken to install and remove pipe tapping apparatus;
v) the long-term stability of the branch fitting tapped into a pipe, especially around the joint between the branch fitting and the main pipe;
vi) difficulties associated with removal of the `coupon` or `slug` portion cut from the pipe.
An indication of the state of the art is provided by European Patent Application EP 0,754,900 A1, entitled "Tapping Fitting", which discloses a tapping tee fitting for application to a pipe in order to tap a fluid conducted therethrough to an ancillary device. The tapping fitting includes a housing having a rotatable blade assembly which is threadedly received within the housing main section, and includes a cylindrical cutting blade at its inner end which may be employed to cut a cylindrical slug from the pipe. The device further includes a hollow stem secured to the rotatable assembly. An outlet section is positioned generally transversely to the housing main section so that it rests generally above and perpendicular to the area of the pipe which is sought to be tapped. In operation, a key is used to rotate the hollow stem and blade assembly from an initial retracted position to a projected position which represents completion of the cutting operation. Thereafter, the cutter blade assembly is rotated in the opposite direction within the hollow stem so as to retract the cutter assembly from its engagement with the pipe. The key may then be removed and the hollow stem is detached so as to leave the cutter assembly retained in the housing main section.
Whilst the above device describes a comprehensive tapping fitting for use in tapping a fluid through to an ancillary device, the threaded nature of the rotatable blade assembly and the cylindrical cutting blade, would appear to compound the resistive forces which arise during the cutting process, thereby limiting the usefulness of the device in respect of pipes which feature large diameters, thick pipe walls, and/or materials difficult to penetrate.